Examining Clear-Air Turbulence Cases in the Northeast Corridor

• Alexandra Vannatta, Meteorology and Climatology, University of Delaware

• Shuai Wang, College of Earth, Ocean and Environment, University of Delaware

Clear-air turbulence (CAT) occurs in clear skies at high altitudes at or above 15,000 feet and is one of the hardest-to-predict weather phenomena associated with aviation. It forms outside of convective storms and often without visible signs, making it difficult for meteorologists to detect and pilots to avoid. To better understand and forecast CAT, meteorologists Gary Ellrod and David Knapp developed the Ellrod Index, which calculates the potential for CAT occurrence based on vertical wind shear and horizontal deformation (Ellrod and Knapp, 1992). This study evaluated the performance of the Ellrod Index by using two CAT case studies and comparing these cases to a calculated 6-year climatology. The Ellrod Index calculations for both events and the 6-year climatology were derived from the European Centre for Medium-Range Weather Forecasts Reanalysis v5 (ERA5) data. The log-transformed Ellrod values were then analyzed to determine whether the Ellrod Index was a reliable indicator of CAT potential, and to evaluate the contributions of horizontal deformation and vertical wind shear. The two case studies analyzed were over the Northeast Corridor (39-41°N, -77- 73°W) to obtain an understanding of regional climate and CAT patterns. The results suggest that the Ellrod Index successfully identified regions where significant CAT occurred. They show that horizontal deformation contributed more strongly than vertical wind shear in both case studies.